Mutations conferring self-compatibility in Prunus species: From deletions and insertions to epigenetic alterations

• Self-incompatibility is found in several Prunus species.
• Self-compatibility is an interesting horticultural trait.
• Self-compatibility may be due to a diversity of mutations.
• These mutations may affect the stylar or the pollen part.
• These mutations include deletions, insertions, shift mutations and epigenetic changes.

Self-incompatible Prunus species show a gametophytic self-incompatibility system, but self-compatibility is an interesting horticultural trait in these fruit tree species. Self-compatibility has recently attracted a particular attention since molecular approaches have been applied to the elucidation of the interacting pollen–pistil mechanism and to the identification of the genes involved in pistil–pollen recognition. Both mutations of the S-RNase gene expressed in the pistil and the SFB gene expressed in the pollen have been reported to explain breakdown of the incompatibility system in Prunus. Stylar-part mutations have revealed that ribonuclease activity of the S-RNases is required to inhibit pollen growth and have shown different activity levels for some S-RNases. The self-compatibility observed in some cultivars has been reported to be due to a defective pollen S-function, such as in sweet cherry, apricot, Japanese apricot and peach. Breakdown of self-incompatibility has also been associated with mutations affecting modifier genes unlinked to the S-locus, such as in sweet cherry, apricot, Japanese plum, and almond. Additionally, a double phenotypic expression of the same S-genotype has been observed in Japanese plum, sweet cherry and almond. The nature of these different mutations has only been identified in a few cases, including deletions, insertions, shift mutations and, more recently, epigenetic alterations.